USR Stiletto

[DPatell]

Elastic belong in your underwear, unless it's on fire.

 

[jetra2]

Agreed. I'll use elastic on anything 2" or less in LPR and MPR. Kevlar cord or TN for the rest.

Also, I agree with the diagnosis that epoxy construction may have prevented the fin from coming off.

Jason

 

[KarlD]

I have built several USR kits and the use of Tiebond II for a paper to paper or wood works well. If you follow the instructions to fillet the fins three times with Tiebond II, in my exp, the joint is as strong as epoxy, only lighter.
The only downside is that the Tiebond II fillets take about 8 hours to dry. Plus they have bubbles so they are not as nice looking as an epoxy joint...but they are strong.

 

[rstaff3]

Elastic size properly and attached to a fire-proof tether happens to work quite nicely even for large MPR and small HPR birds.

 

[Jerry Irvine]

Originally posted by jetra2
Agreed. I'll use elastic on anything 2" or less in LPR and MPR. Kevlar cord or TN for the rest.

Also, I agree with the diagnosis that epoxy construction may have prevented the fin from coming off.

Jason

Maybe, but this way it is easily repairable. That matters.

As for alternate shock line methods, we have experimented with several, including U-bolts with nylon on large rockets.

But for low-mid-power we are still looking for a good alternative to 3-fold and elastic.

Jerry

 

[lalligood]

Originally posted by Jerry Irvine
But for low-mid-power we are still looking for a good alternative to 3-fold and elastic.

Classic example of "if it ain't broke, then don't fix it"

 

[rstaff3]

For larger elastic, the NCR Gorilla Mount method works great. Basically a steel leader thru the top CR. I've certainly never tried the three fold method on large elastic. I suspect epoxy to the airframe is better.

 

[Jerry Irvine]

Originally posted by rstaff3
For larger elastic, the NCR Gorilla Mount method works great. Basically a steel leader thru the top CR. I've certainly never tried the three fold method on large elastic. I suspect epoxy to the airframe is better.

NCR was a failed product line for a variety of reasons.

We have recommended epoxying shock cords directly to the wall and that works great. Any new method should allow for less heat damage and replaceable parts.

Jerry

 

[rstaff3]

Can't comment on NCR's issues. However the Gorilla Mount was good. It wouldn't burn, moved the elastic cord away from the heat and made said cord replacable too. I just made a clone using the wire cable form the garage door spring that I just replaced

I'm remembering something, from somewhere, maybe related to hanging pictures on walls. It consisted of some tough material maybe cloth, which had an intergral hook built in. Maybe something similarcould be used for rockets - use a D-ring, and epoxy it to the wall part way down the tube?

 

[DPatell]

Lets see...3 fillets of titebond so it will easily fall apart, but will also be easy to put together...or one fillet of 30 minute epoxy that is solid, will not break, so you don't have to fix it.

also, 5 feet of elastic glued to the inside of the tube, so it's easy to fix...or 15' of Kevlar to an eyebolt/u-bolt on the top CR, never have to replace...

The choices are simple to me, epoxy and kevlar.

Why build something that is easy to replace, when there is an alternate method that is easier and will last longer than the rocket? USR's philosophy is out there.

If I am going to put time into a rocket, the last thing I want to happen is the shockcord breaking or a fin getting snapped off at deployment, even if I can say "oh, it was sorta built for that to happen, I will glue it back together."

 

[lalligood]

Originally posted by rstaff3
I'm remembering something, from somewhere, maybe related to hanging pictures on walls. It consisted of some tough material maybe cloth, which had an intergral hook built in. Maybe something similarcould be used for rockets - use a D-ring, and epoxy it to the wall part way down the tube?

There's a guy in my club that uses fishing leader epoxied to the inside of the tube and forms it into a loop that peeks out just over the end of the tube then ties the shock cord onto that. The loop folds back down into the tube when prepping the rocket for flight. I've never tried this so I don't know if and/or how well it would scale up but I'll throw it out there for the discussion...

 

[rstaff3]

Originally posted by DPatell
Lets see...3 fillets of titebond so it will easily fall apart, but will also be easy to put together...or one fillet of 30 minute epoxy that is solid, will not break, so you don't have to fix it.

also, 5 feet of elastic glued to the inside of the tube, so it's easy to fix...or 15' of Kevlar to an eyebolt/u-bolt on the top CR, never have to replace...

The choices are simple to me, epoxy and kevlar.

Why build something that is easy to replace, when there is an alternate method that is easier and will last longer than the rocket? USR's philosophy is out there.

If I am going to put time into a rocket, the last thing I want to happen is the shockcord breaking or a fin getting snapped off at deployment, even if I can say "oh, it was sorta built for that to happen, I will glue it back together."

I build some of my MPR rockets this way, but not every MPR rocket needs heavy hardware and relatively expensive Kevlar.

 

[Jerry Irvine]

Looking at what some folks have done and assuming I limit the choices to yellow glue compatible solutions, the two I have seen with promise are Kevlar braid glued to the side of the motor tube with a loop on the end.

The other is a steel line looped on one end and studded on the other.

Several problems.

These are MANY, MANY times the cost of the current system. The minimum order for these parts for any decent kit run is 20,000.

That many tri-folds is trivial cost. Either Kevlar with a loop or steel with a loop and a stud are far more expensive (and labor intensive or hard to source) and limited to specific tube lengths and motor mount placements. They are NOT universal.

Making ONE of anything is easy. Making 20,000 of anything is HARD.

Jerry

 

[KermieD]

Fishing leaders are basically a steel loop. A knot and/or light dab of JB Weld (or solder) on one end is a stud. Cheap, easy and effective. JB Weld is not yellow glue, true, but certainly a BB sized ball of it against the MMT will not affect performance as an epoxy build would. I agree that Kevlar is a rather pricey solution.

 

[KarlD]

What would the costs be for just a lenght of Kelvar braded cord included with the kits? Prehaps include a "Quick-link" and have the kit-builder tie it all together.

I know that it would be more thqn the "tri-fold" system, but I have had great success with this system on my USR kits...

Prehaps just the Kelvar, and let the person add a "Quick-Link" if desired would be the best cost-effective solution.

Just chucking out idea...

 

[DPatell]

If that's the case, why should I sacrifice quality and correctness of parts in USR, when I can get top notch, bullet proof kits from PML?

 

[AlexM]

Because PML kits arent built to be light. They are pretty much made to be overbuilt. A USR kit is made to go high and fast. You start using epoxy, and you get a lot of uneeded weight when it is so much lighter to use wood glue.

 

[rstaff3]

Please take time and think about how you phrase your comments. I don't want this to become a bashing contest. It's clear there are different design philosophies with different goals. Ultimately sales will tell who is right and wrong, or if both have their place.

 

[Jerry Irvine]

Comparing "benefits" seems totally on-topic.

A kit should be turn-key, so if use of kevlar or fishing leaders requires a quick link, then it must be included.

I know this from experience. The cost to produce a typical TN/QL/UB recovery harness is about the same as an entire 24mm kit.

So any "upgrade" to typical Banshee kit recovery should at minimum be "better" and "turn-key", and preferably also not 5x the cost.

Jerry

 

[rstaff3]

Originally posted by Jerry Irvine
Comparing "benefits" seems totally on-topic.

Agreed. My comment wasn't intended to stifle the discsussion, just to make sure it stays constructive.

 

[KarlD]

Originally posted by rstaff3
Please take time and think about how you phrase your comments. I don't want this to become a bashing contest. It's clear there are different design philosophies with different goals. Ultimately sales will tell who is right and wrong, or if both have their place.

Good point...

I have a PML kit and a USR kit of about the same size. If both units would lawn-dart, The PML would probably fare MUCH better than the USR kit. However, the USR kit is half the weight, and goes much HIGHER in altitude with the same motor load as the PML kit.

It's just a question of design styles.... I personally prefer preformace over bulletproof. If I have my ducks in a row, I do not need bulletproof. If I do not...Well I have had a good learning experience.

 

[KarlD]

Originally posted by DPatell
Lets see...3 fillets of titebond so it will easily fall apart, but will also be easy to put together...or one fillet of 30 minute epoxy that is solid, will not break, so you don't have to fix it.

The 3 fillets of TieBond II are stronger than the paper and plywood. From personal experience with a Through-the-wall mount crash from too much delay time, the bodytube fails before the Tiebond II fillet joint.

Now a Quantium-G-22 fillet joint? Epoxy with milled fiberglass and/or microballons filler all of the way. Completely different materials. And a severe weight increase.

 

[Jerry Irvine]

I have noticed Lance Alligood's review of his USR Stiletto has been updated at EMRR.

I also left a comment.

Jerry

 

[firemanup]

"Looking at what some folks have done and assuming I limit the choices to yellow glue compatible solutions, the two I have seen with promise are Kevlar braid glued to the side of the motor tube with a loop on the end."

Like it and use it alot... Jerry i have no clue about mass pricing but what about supplying a 36" or 48" piece of the smaller braided kevlar stuff with each kit.. then the builder can cut to fit..? Or does that go back to over pricing the kit...?

"If that's the case, why should I sacrifice quality and correctness of parts in USR, when I can get top notch, bullet proof kits from PML?"

Dpatell,

PML kits are NOT bulletproof. My 4" Amraam went up and came back down on the stock chute and sheared one of the bottom fins upon landing, it now has a 3/4" tear in the base of it just above the fillet. The fillet was strong enough to hold and the next weakest part was the fin which tore.

AT makes their kits for this very issue.. if built per the instructions with Med CA this very same scenario the fin pops out of the fin lock system and is then easily re-glued and replaced without any further problem..

For me to replace my PML fin now i'd have to cut it out, and when it's secured with internal fillets to both the motor mount and the inside of the body tube i have no idea how i could do that without tearing the fin can apart..??

Some scenarios the easy repair is more beneficial..

 

[lalligood]

Originally posted by Jerry Irvine
I have noticed Lance Alligood's review of his USR Stiletto has been updated at EMRR.

I also left a comment.

Jerry

And thank you very much for the nice words

 

[Jerry Irvine]

Originally posted by firemanup
what about supplying a 36" or 48" piece of the smaller braided kevlar stuff with each kit.. then the builder can cut to fit..?

Firstly, thank you for the first positive post toward me I can ever remember from you.

Secondly, that seems practical if tying a loop/knot does not make the kevlar line too weak for use.

Also sourcing the "proper" kevlar form in bulk is problematic because Kevlar is still a small scale commodity.

I am open to Kevlar bulk supplier suggestions.

I have about 10 inadequate sample rolls right now.

Jerry

 

[firemanup]

Jerry quit already....

The thread isn't positive toward you or anyone else.. it's just my opinions and ideas in a civil manner..

We've communicated plenty before in a civil manner before this as is evidenced here..

https://www.rocketryforum.com/showthread.php?s=&threadid=13852&highlight=mach

In that thread i followed your advice months ago in how I airfoiled my fins, because you have more experience and were willing to share it with me i took your advice because you were right.. thanks by the way.. it's turned out great..

I enjoy your civil converstations on here as i think you've got information/knowledge to share..thanks for when you share it..

As far as the knot on the tubular kevlar being too weak... i think a figure 8 on a bite with 1/8" tubular kevlar would have plenty of strength for most of your 4" or under body tubes as you tend to design your birds to be minimal in weight... i can't see the kevlar or knot being the weakest parts...

As far as suppliers of kevlar i get all mine from Giant leap maybe they could supply to you or suggest sources for a vendor..

By the way did you get my private message a couple weeks ago..?